A play about nuclear arms negotiations in the 1980s should be a dated piece of interest only to historians of theatre, and perhaps, of nuclear strategy. Lee Blessing’s “A Walk in the Woods” is as relevant today as it was when it was written almost 30 years ago, though. For one thing, our world hasn’t grown out of nuclear threats, a disappointment felt heavily by those of us who thought the end of the Cold War might mean something better. More importantly, though, Blessing’s script isn’t about throw-weights, megadeaths, SLCMs, ICBMs, Pershing IIs and SS-20s (I’ll spare you the definitions,